This invention relates to meridian seeking gyroscopic instruments and, more particularly, to an effective damping arrangement for such an instrument.
H. N. Eklund Reissue U.S. Pat. No. 26,370, which issued Apr. 9, 1968, discloses a meridian seeking instrument comprising a gyroscope unit hanging in a container from a thin suspension band. The suspension band supports the gyroscope unit so it is able to rotate about a vertical axis relative to the container. However, the suspension band exerts a restoring torque on the gyroscope unit responsive to the angular displacement of the gyroscope unit about the vertical axis from a reference position relative to the container. The gyroscope unit has a horizontal spin axis that tends to align itself with the meridian. The container is rotatably supported about the vertical axis. A transducer generates a control signal representative of the angular displacement between the ggyroscope unit and the container about the vertical axis from the reference position. A motor rotates the container about the vertical axis responsive to the control signal so as to reduce the angular displacement from the reference position. Thus, as the gyroscope unit aligns itself with the meridian the container follows it and untwists the suspension band.
Ideally, the gyroscope unit would be completely unconstrained by the suspension band as it moves about the vertical axis under the influence of the earth's spin. Accordingly, from the point of view of accuracy of the instrument, it is desirable for the torsional spring constant of the suspension band, i.e., the ratio of restoring torque to angular displacement, to be as small as practicable. However, the suspension band is the only effective means for dissipating the rotational energy of the gyroscope unit about the vertical axis. Accordingly, from the point of view of restraining the oscillations of the gyroscope unit about the vertical axis, it is desirable for the torsional spring constant of the suspension band to be as large as practicable. Thus, in selecting the torsional spring constant for the suspension band a compromise must be struck between accuracy and damping.